A typical conventional structure for connecting links of a band made of metal plate is described with reference to FIG. 12. The figure is an exploded perspective view of a part of the band, drawn to show the underside thereof upward.
A link 60 is formed by shaping a metal plate cut and machined beforehand into a square tube, and comprises three annular portions 61, 62 and 63 at the ends and the center thereof, and connecting portions 64 connecting the annular portions. An engaging recess 66 is formed at the inner portion of the annular portion 63 provided at the end. When the link 60 is formed into the tube, a core 67 is wrapped in and clasped by the other annular portion 61 so as to block the opening of the link 60, hence being secured therein. A connecting link 68 has a gap 70 through which the connecting portion 64 of the link is inserted, thereby sequentially connecting the links 60.
A connecting member 71 substantially has a U-shape, and comprises a base 72, engaging projection 73 formed on the axis of symmetry, and a pair of connecting arms 74. The connecting member 71 is inserted into the inner space of the link 60 from an end opening 75. The engaging projection 73 renders an abutting portion 76 adjacent the annular portion 63 to slightly yield, overcoming the resistance thereof, and then engages in an outer end portion of the engaging recess 66, thereby preventing disengagement. During the course of insertion, each of the connecting arms 74 penetrates the two of the adjacent two pairs of connecting links 68, so that the connection of each link is completed.
In the conventional structure, in order to remove or add a link to adjust the length of the band, a part of the connected links must be temporarily disengaged. In order to detach a link, a rod-shaped tapered tool 77 is diagonally inserted in the engaging recess 66 of the link 60 as shown in the drawing, and forcefully pushes the bottom of the U-shape of the connecting member 71 in the outer direction. Thus, the connecting member 71 is pushed outward from the band. The engaging projection 73 overcomes the resistance of the abutting portion 76 and is forced outward. The connecting member 71 is then taken out by such a tool as pliers. Thus the link can be detached.
During the detaching operation, the tool 77 is pushed diagonally so that the effective force for pushing out the connecting member 71 is a horizontal component of the pushing force exerted by the tool 77, amounting only to several tens of percentages thereof. Although there is also generated a normal component of the pushing force amounting to several tens of percentages thereof, such a force increases the coefficient of friction between the connecting member 71 and the link so that the pulling force must be increased. When the tool 77 is inserted at an angle of 45.degree., horizontal and normal component are each about 71 percent of the pushing force exerted by the tool. In addition, the engaging projection 73 must cover a long distance to overcome the abutting portion 76. Namely, a large operating force and a relatively long stroke must be applied to the tool 77, and it is difficult to pull out the connecting member 71, and the tool may slip, causing a damage to the band.
Furthermore, in the conventional structure, the engaging recess 66 and the engaging projection 73 engaged with the recess 66 are apparent from the underside of the band, thereby deteriorating the appearance of the underside of the band. In addition, the engaging recess 66 gives a rugged feel to the wrist or catches the skin and hair, so that the band cannot be comfortably worn.
An object of the present invention is to provide a structure for connecting links of a band formed by shaping a metal plate, wherein the above described defects of the conventional structure are overcome, so that the connecting member can be pulled out with a small force, the appearance of the underside of the band improved, and the width of the band can be decreased.